This K23 application seeks support essential to my development as a patient oriented clinical investigator able to design, execute, and evaluate, theory-driven explanatory randomized clinical trials (RCTs). I am building a multi-method program of research to study how parents are drawn into accommodating their child's anxiety, and to intervene by modifying these patterns of enmeshment. I have conducted small clinical trials and have examined key biological and behavioral parent markers. I need to develop my skill and expertise in three core areas: 1) Designing and executing explanatory RCTs~ 2) Integrating bio-behavioral markers in explanatory RCTs~ 3) Applying statistical methods to test hypotheses of mediation and moderation in explanatory RCTs. To achieve these goals I have developed a training plan including regular meetings with all my sponsors, visits to other laboratories, courses seminars and workshops, independent reading, and scientific meetings. The superb and dedicated mentorship team ensures I receive strong, state of the art training. Their mentorship, the training activities, and the outstanding academic environment at the Yale Child Study Center, will provide me with the skills to launch an independent research career, starting with my first R01. The role of parents in the treatment of childhood anxiety remains unresolved. Including parents in the treatment process has not yielded superior effects compared to individual cognitive behavioral therapy (ICBT). One plausible conclusion from these data is that parent work cannot enhance effects treatment effects. This K23 focuses on an alternative plausible conclusion: That parent interventions need to be informed by theoretical working models of parent-specific mechanisms of change that are not targeted in ICBT~ and that parent interventions need to be evaluated in explanatory clinical trials asking not only 'doe treatment work?' but also 'how and for whom does treatment work?' Underlying systems that shape parents' responses to child anxiety provide clues to such parent-specific targets for intervention, and point to potential mediators and moderators of treatment response. Identifying mediators and moderators of response to parent interventions can enhance child anxiety outcomes and advance the goal of personalized psychotherapy. The SPACE Program (Supportive Parenting For Anxious Childhood Emotions) is a parent-based intervention that targets family accommodation (FA), of child anxiety. I propose an integrated explanatory clinical trial of SPACE, with ICBT as baseline comparison condition. The trial asks 3 main questions: 1) Will SPACE lead to significantly lower levels of FA compared to ICBT? 2) Will reducing FA lead to positive child outcomes? 3) Will key biological and behavioral markers (i.e., maternal oxytocin, autonomy granting, over involvement, sensitivity) moderate child outcomes? Children aged 7-14 (n=120), with primary anxiety disorders, will be randomized to either ICBT or SPACE. Results of this trial will guide the preparation of an R01 and have the potential to enhance treatment outcomes for the highly prevalent child anxiety disorders.